An optical fiber base material, which will become an optical fiber by being drawn, is manufactured by undergoing a core-portion manufacturing process of forming a core portion having a high refractive index, and a clad-portion manufacturing process of forming a clad portion on an outer surface of the core portion resulting from the core-portion manufacturing process, where the clad portion has a refractive index lower than the refractive index of the core portion.
FIG. 1 schematically shows a core-portion manufacturing apparatus 100 employed in the core-portion manufacturing process. When a raw material gas that contains SiCl4 and GeCl4 is supplied into a burner 21 within a process chamber 11 together with a combustion gas that contains hydrogen and oxygen, GeO2 doped glass particles SiO2 are generated by means of flame hydrolysis such as shown in the following equation:SiCl4+2H2O=SiO2+4HClGeCl4+2H2O=GeO2+4HCl
Thus generated glass particles are attached and deposited to a tip of a starting target material 30 rotating within the process chamber 11. In view of this, a tip of an object created by deposition is monitored by means of a monitor 55 to perform feedback control. Then according to the growth of the deposition object, the starting target material 30 is pulled out. In this way, a porous core base material 40, in which glass particles aggregate, is formed. During this process, unattached glass particless will be discharged through an exhaust tube 51 to outside the system.
On the other hand, the porous core base material 40 after undergoing the deposition process is subjected to a sintering process where dehydration and vitrification into transparent glass are performed, thereby being completed as a core base material. This core base material is sometimes made from a material of the core portion solely, or is made from combination of a material corresponding to a part of the clad portion and the material of the core portion in other times.
FIG. 2 schematically shows a clad-portion manufacturing apparatus 200 employed in the clad-portion manufacturing process performed by using a core base material 70 manufactured in the core manufacturing process. First, dummy glass rods 61 and 62 are fusion-bonded to both ends of the core base material 70 elongated into prescribed length and diameter, to prepare a starting glass rod.
Next, a raw material gas containing SiCl4 is supplied together with a combustion gas containing hydrogen and oxygen into one or more burners 22 within the process chamber 12 in which the starting glass rod is being rotated, thereby generating glass particles. Thus generated glass particles are deposited on the outer surface of the core base material 70 of the starting glass rod. During this process, by reciprocation of the burners 22 along the axial direction of the core base material 70 as shown by the arrow in the drawing, the glass particles are deposited to the entire length of the core base material 70 uniformly.
FIG. 3 shows an optical fiber base material 30 obtained in the above way. As shown in this drawing, a porous base material 80 is formed on the outer surface of the core base material 70. Note that glass particles not attached to the porous base material 80 are discharged through an exhaust tube 52 of the clad-portion manufacturing apparatus 200 (shown in FIG. 2) to outside the system. In addition, the porous base material 80 after undergoing the deposition is subjected to the next sintering process where dehydration and vitrification into transparent glass are performed, thereby being completed as an optical fiber base material.